Generally, an exhaust gas purification system is used which includes an exhaust gas purification device which has catalyst devices such as an oxidation catalyst, a device (DOC), a particulate collection device (CSF, SCRF, and the like), a selective reduction catalyst (SCR) device, and a lean NOx trap catalyst device (LNT) to purify purification object components such as hydrocarbon (HC), carbon monoxide (CO), particulate substance (PM), and nitrogen oxide (NOx) included in exhaust gases of the internal combustion engine such as a diesel engine.
In the exhaust gas purification system, a temperature-rising control of the exhaust gas is regularly performed for the release and the reduction (NOx regeneration) of NOx stored in the lean NOx trap catalyst device, the combustion-removal (PM regeneration) of the particulate substance collected in the particulate collection device, the removal (sulfur purge) of the sulfur component accumulated in various catalyst devices such as an oxidation catalyst device or the lean NOx trap catalyst device, and the like.
In the related art, at the time of the temperature-rising control of the exhaust gas, a detection temperature of an exhaust gas temperature sensor provided in the vicinity of any one catalyst device in the catalyst devices, and the estimation temperature of any one catalyst device obtained by following methods are set as a control temperature which is a control value of a feedback control with respect to a target temperature of the exhaust gas in the temperature-rising control. In the case of some catalyst devices, normally, in view of responsiveness, the temperature relating to the catalyst device in which the heat generation amount by the combustion of unburned hydrocarbon (HC) supplied to increase a temperature is largest is used as the control temperature steadily.
With respect thereto, as described, for example, in Japanese Unexamined Patent Application Publication No. 2013-174203, an exhaust gas purification device is proposed which includes a selective reduction catalyst, a particulate filter which is arranged on the exhaust gas upstream side from the selective reduction catalyst and in which an oxidation catalyst layer is formed to further collect the particulate in the exhaust gas, a liquid injection nozzle through which the hydrocarbon based liquid can be injected toward the particulate filter, and a liquid feeding unit which supplies the liquid to the liquid injection nozzle. In the exhaust gas purification device which purifies the exhaust gas of the engine, the temperature of the exhaust gas relating to the particulate filter is detected using a temperature sensor, and the liquid feeding unit is controlled on the basis of a detection output of the temperature sensor.
However, in a zone-coat and the like in which a plurality of catalyst devices or the catalyst layers are coated for each part in separate colors, a place (catalyst device) in which the heat generation amount is largest in the exhaust passage may be different according to an operating condition of the engine. For example, in the case of a system which is configured by the oxidation catalyst device, the lean NOx trap catalyst device, and the particulate collection device, when an excess air ratio λ in the exhaust gas is high, and the concentration of the oxygen is high, the most hydrocarbon is combusted by the oxidation catalyst device on the upstream side to generate beat. For this reason, in the lean NOx trap catalyst device or the particulate collection device on the downstream side, the temperature of each catalyst device is increased not by the generation of the combustion heat of the hydrocarbon, but by the heat transmission of the exhaust gas of which the temperature is increased by the oxidation catalyst device.
On the other hand, in a case where the excess air ratio of the exhaust gas is low and the concentration of the oxygen is low such as the sulfur purge (S purge: sulfur purge) control or rich combustion of NOx regeneration, the combustion of the hydrocarbon is caused using the oxygen adsorbed in the lean NOx trap catalyst device or the oxygen generated by NOx reduction, and thus the generation amount of the combustion heat of the hydrocarbon in the lean NOx trap catalyst device is larger than that in the oxidation catalyst device.
Similarly, in the case of the exhaust gas purification system configured by a plurality of catalyst devices in combination, a place in which the generation amount of the fuel heat is largest is changed according to the operating condition of the engine. Therefore, as in the related art, when the control temperature at the time of the temperature-rising control is fixed to a temperature relating to a specified catalyst device such as the catalyst device in which the heat generation amount due to the combustion of the hydrocarbon is largest, an insufficient temperature increment, an overshooting at the time of increasing a temperature, erosion, and the like may be occur according to the operating condition of the engine in another catalyst device other than the specified catalyst device.